Multi-Dimensional Arrays

1
Multi-Dimensional Arrays
2
A Table of Values

Balances for Various Interest Rates Compounded Annually (Rounded to Whole Dollar Amounts) Balances for Various Interest Rates Compounded Annually (Rounded to Whole Dollar Amounts) Balances for Various Interest Rates Compounded Annually (Rounded to Whole Dollar Amounts) Balances for Various Interest Rates Compounded Annually (Rounded to Whole Dollar Amounts)
Year 5.00 5.50 6.00
1 1050 1055 1060
2 1103 1113 1124
3 1158 1174 1191
3
Row and Column Indices for an Array

Indices 0 1 2
0 1050 1055 1060
1 1103 1113 1124
2 1158 1174 1191
4
Multi-Dimensional Array Basics

• We declare a variable, table, to be a
  two-dimensional array as follows
• int table new int 106
• This is the same as for one-dimensional arrays
  except we use a second pair of square brackets in
  two places.
• You can have arrays of any number of dimensions.

5
Multi-Dimensional Array Basics (contd)

• In a two-dimensional array we consider the first
  index to represent the row number and the second
  to represent the column.
• As was true of the indexed variables for
  one-dimensional arrays, indexed variables of
  multi-dimensional arrays are variables of the
  base type and can be used anyplace that a
  variable of the base type is allowed.

6
Example of Using a Two-Dimensional Array

• / Displays a two-dimensional table showing
  how interest rates affect bank
  balances./public class InterestTable
  public static void main(String args)
  int table new int106 int row,
  column for (row 0 row lt 10 row)
  for (column 0 column lt 6 column)
  tablerowcolumn
  balance(1000.00, row 1, (5 0.5column))
  System.out.println("Balances for Various
  Interest Rates") System.out.println("Compou
  nded Annually") System.out.println("(Rounde
  d to Whole Dollar Amounts)")
  System.out.println("Years 5.00 5.50 6.00 6.50
  7.00 7.50") System.out.println( )
  for (row 0 row lt 10 row)
  System.out.print((row 1) " ")
  for (column 0 column lt 6 column)
  System.out.print("" tablerowcolumn "
  ") System.out.println( )
  

7
Example of Using a Two-Dimensional Array (contd)

• / Returns the balance in an account that
  starts with startBalance and is left for the
  indicated number of years with rate as the
  interest rate. Interest is compounded annually.
  The balance is rounded to a whole number.
  / public static int balance(double
  startBalance, int years, double rate)
  double runningBalance startBalance int
  count for (count 1 count lt years
  count) runningBalance
  runningBalance(1 rate/100) return (int)
  (Math.round(runningBalance))

8
Multi-Dimensional Array Parameters and Returned
Values

• Methods may have multi-dimensional array
  parameters and may return a multi-dimensional
  array.
• The situation is similar to that of the
  one-dimensional case, except that you use more
  square brackets.

9
Example Using a Multi-Dimensional Array Parameter

• / Displays a two-dimensional table showing
  how interest rates affect bank
  balances./public class InterestTable2
  public static void main(String args)
  int table new int106 int row,
  column for (row 0 row lt 10 row)
  for (column 0 column lt 6 column)
  tablerowcolumn
  balance(1000.00, row 1, (5 0.5column))
  System.out.println("Balances for Various
  Interest Rates") System.out.println("Compou
  nded Annually") System.out.println("(Rounde
  d to Whole Dollar Amounts)")
  System.out.println("Years 5.00 5.50 6.00 6.50
  7.00 7.50") System.out.println( )
  showTable(table)

10
Example Using a Multi-Dimensional Array Parameter
(contd)

• / Precondition The array displayArray
  has 10 rows and 6 columns. Postcondition
  The array contents are displayed with dollar
  signs. / public static void
  showTable(int displayArray) int
  row, column for (row 0 row lt 10
  row) System.out.print((row
  1) " ") for (column 0 column
  lt 6 column) System.out.print(""
  displayArrayrowcolumn " ")
  System.out.println( ) public
  static int balance(double startBalance, int
  years, double rate) double
  runningBalance startBalance int count
  for (count 1 count lt years count)
  runningBalance runningBalance(1
  rate/100) return (int) (Math.round(runningB
  alance))

11
Implementation of Multi-Dimensional Arrays

• In Java, multi-dimensional arrays are implemented
  using one-dimensional arrays.
• The array table declared as follows
• int table new int106
• is a one-dimensional array of length 10 whose
  elements are one-dimensional arrays of length 6.
• In other words, multi-dimensional arrays are
  arrays of arrays.

12
The Method showTable Redefined

• / The array displayArray can have any
  dimensions. Postcondition The array contents
  are displayed with dollar signs./public static
  void showTable(int displayArray) int
  row, column for (row 0 row lt
  displayArray.length row)
  System.out.print((row 1) " ") for
  (column 0 column lt displayArrayrow.length
  column) System.out.print(""
  displayArrayrowcolumn " ")
  System.out.println( )

13
Programming Example Using Multi-Dimensional Arrays

• / Class for a one-week record of the time
  worked by each employee. Uses a five-day week
  (Mon.-Fri.). main has a sample
  application./public class TimeBook
  private int numberOfEmployees private
  int hours //hoursij has the
  hours for employee j on day i. private int
  weekHours //weekHoursi has the weeks
  hours worked for //employee i1.
  private int dayHours //dayHoursi
  has the total hours worked by all
  //employees on day i. Monday is 0, Tuesday 1,
  etc. / Reads hours worked for
  each employee on each day of the week into
  the two-dimensional array hours. (The method
  for input is just a stub in this preliminary
  version.) Computes the total weekly hours
  for each employee and the total daily hours
  for all employees combined. / public
  static void main(String args)
  TimeBook book new TimeBook(3)
  book.setHours( ) book.update( )
  book.showTable( )

14
Programming Example Using Multi-Dimensional
Arrays (contd)

• public TimeBook(int theNumberOfEmployees)
  numberOfEmployees theNumberOfEmployees
  hours new int5numberOfEmployees
  //the 5 is for the 5 days Monday through
  Friday. weekHours new
  intnumberOfEmployees dayHours new
  int5 public void setHours( ) //This
  is just a stub. hours00 8
  hours01 0 hours02 9
  hours10 8 hours11 0 hours12
  9 hours20 8 hours21 8
  hours22 8 hours30 8
  hours31 8 hours32 4
  hours40 8 hours41 8 hours42
  8 public void update( )
  computeWeekHours( ) computeDayHours(
  )

15
Programming Example Using Multi-Dimensional
Arrays (contd)

• private void computeWeekHours( )
  int dayNumber, employeeNumber, sum for
  (employeeNumber 1 employeeNumber
  lt numberOfEmployees employeeNumber)
  //Process one employee sum 0
  for(dayNumber 0 dayNumber lt 5
  dayNumber) sum sum
  hoursdayNumberemployeeNumber - 1
  //sum contains the sum of all the hours
  worked //in one week by employee
  with number employeeNumber.
  weekHoursemployeeNumber - 1 sum
  private void computeDayHours( )
  int dayNumber, employeeNumber, sum
  for (dayNumber 0 dayNumber lt 5
  dayNumber) //Process one day (for all
  employees) sum 0 for
  (employeeNumber 1
  employeeNumber lt numberOfEmployees
  employeeNumber)
  sum sum hoursdayNumberemployee
  Number - 1 //sum contains the
  sum of all hours worked by all
  //employees on day dayNumber.
  dayHoursdayNumber sum

16
Programming Example Using Multi-Dimensional
Arrays (contd)

• public void showTable( ) int row,
  column System.out.print("Employee ")
  for (column 0 column lt
  numberOfEmployees column)
  System.out.print((column 1) " ")
  System.out.println("Totals")
  System.out.println( ) for (row 0 row
  lt 5 row)
  System.out.print(day(row) " ")
  for (column 0 column lt hoursrow.length
  column) System.out.print(hoursr
  owcolumn " ")
  System.out.println(dayHoursrow)
  System.out.println( )
  System.out.print("Total ") for
  (column 0 column lt numberOfEmployees
  column) System.out.print(weekHoursc
  olumn " ") System.out.println( )
  

17
Programming Example Using Multi-Dimensional
Arrays (contd)

• //Converts 0 to "Monday", 1 to "Tuesday" etc.
  //Blanks used to make all strings the same
  length. private String day(int dayNumber)
  String dayName null switch
  (dayNumber) case 0
  dayName "Monday "
  break case 1
  dayName "Tuesday " break
  case 2 dayName
  "Wednesday" break
  case 3 dayName "Thursday "
  break case 4
  dayName "Friday "
  break default
  System.out.println("Fatal Error.")
  System.exit(0) break
  return dayName